Many different types of property protection alarm systems for protecting property against intrusion and similar alarm conditions are presently known and available. Some of these known alarm systems include a code combination unit for arming and disarming the alarm circuit in response to the entry of a predetermined code. For example, U.S. Pat. No. 2,855,588, issued to Allen on Oct. 7, 1958, shows a combination lock and burglar alarm having a coder unit for disabling the alarm circuit in response to the sequential operation of a plurality of preselected push buttons within a predetermined time period. The coder unit of the Allen patent is associated with a lock positioned at the entrance to the property. The proper entry of the predetermined code in the coder unit not only disables the alarm system but also enables the operator to unlock the lock and enter the premises. Other known alarm systems also employ coder units similar to the coder unit in the Allen patent to arm as well as to disarm the alarm system. In these other alarm systems, the coder units are often positioned inside the protected property, e.g., inside a residence. In this manner, the alarm system can be armed by an authorized operator before leaving the property by providing, in addition to the coder unit, an exit delay circuit for enabling the authorized operator to leave the premises without setting off the alarm. In addition, it is known to use an entrance delay circuit to enable the authorized operator to reenter the property without setting off the alarm circuit. The delay provided by the entrance delay circuit gives the authorized operator a predetermined time period in which to enter the preselected code in the coder unit and disarm the alarm system. For example, a very complicated and sophisticated arrangement of this type is shown in U.S. Pat. No. 3,978,478, issued to Schmitz on Aug. 31, 1976. As explained in the Schmitz patent, the authorized operator enters the preselected code by actuating the appropriate code keys of the numeric keyboard. Following the expiration of a given time period determined by an exit delay circuit (FIG. 6), the alarm circuit is energized. Likewise, upon returning to the property, the authorized operator is given a limited period of time to enter the preselected code in order to disarm the alarm circuit. During both the exit delay period and the entrance delay period, the alarm circuit remains inactive and no alarm is sounded.
One of the disadvantages of this alarm system is that the occupants of the property are not immediately warned of the intrusion of the property. Such warning occurs only after a given delay period. In addition, the complexity and sophistication of the Schmitz patent makes the alarm system impractical for many applications.
In addition to the coding features provided by the above prior art, other known alarm systems provide an alarm circuit for energizing both an external alarm and a local alarm. For example, the external alarm may be located immediately outside the protected property or may be located at some remote point. Generally, the local alarm is located inside the property in order to warn the occupants of the property of an intrusion or some other alarm condition. One known prior art alarm system shows two different local alarms for enabling the occupants to distinguish between an authorized and an unauthorized intrusion of the property. This alarm system is shown in U.S. Pat. No. 3,544,987, issued to McMann on Dec. 1, 1970. The McMann alarm system is a combination of a coder unit similar to those described above for arming and disarming the alarm circuit and two different audible local alarms. Upon arming the alarm circuit in the McMann patent, the first audible or alert alarm is immediately energized. The energization of the other audible alarm is delayed to permit the authorized operator to leave the property. Henceforth, any intrusion of the property will immediately trigger the alert audible alarm and will trigger the other audible alarm after the expiration of a given delay period. One of the disadvantages of the McMann alarm system is that, although it is desirable to have a local audible alarm immediately energized upon any intrusion of the premises, it is disturbing to the other occupants of the property to have this same audible alarm energized when the alarm circuit is initially armed by the entry of the preselected code. In addition, it is often desirable to locate one of these alarms in an external location rather than centralizing all of the alarms energized by the alarm circuit.
Accordingly, it is an object of the present invention to provide a property protection alarm system which overcomes the disadvantages of the prior art alarm systems described above. In particular, it is an object of the present invention to provide an alarm system having an alarm circuit including both an external alarm and a local audible alarm in which the local audible alarm is only energized in response to an intrusion of the property after the alarm circuit is armed. In addition, it is an object of the present invention to provide an alarm system including a code combination logic circuit for arming and disarming the alarm circuit in response to the entry of a predetermined code in a numeric keyboard. The improved alarm system of the present invention enables an authorized operator to arm the alarm circuit and leave the premises without energizing either the local audible alarm or the external alarm. Then, any subsequent intrusion of the property, including entry by the authorized operator, immediately energizes the local audible alarm to warn other occupants of the property of such intrusion while at the same time providing the authorized operator a given period of time in which to prevent the energization of the external alarm.
Another object of the present invention is to provide an alarm system which is armed by the entry of a predetermined code in a numeric keyboard within a given period of time and in a predetermined sequence. In this regard, it is an object of the present invention to provide a code combination logic circuit requiring the authorized operator, upon entering the predetermined code, to actuate one of the digits of the predetermined code for a given period of time in order to enable the code combination logic circuit to arm the alarm circuit.
It is a further object of the present invention to provide visual display means in proximity to the numeric keyboard for indicating that the alarm system has been armed by the entry of the proper predetermined code.
A final object of the present invention is to provide an automatic periodic test circuit for determining whether the alarm condition which actuates the alarm circuit continues to exist and for automatically deenergizing the local audible alarm and the external alarm circuit if the test circuit determines that the alarm condition has been eliminated.